Fatigue deformation of a superplastic aluminum-zinc eutectoid alloy.

摘要

The fatigue deformation of a superplastic aluminum-zinc eutectoid alloy was investigated at temperatures of 100 and 200;Two techniques were used for studying the surfaces of fatigue tested specimens: transmission electron microscopy of two-stage carbon replicas and scanning electron microscopy. Selected areas on a surface were examined before fatigue deformation and re-examined after fatigue deformation. To investigate the internal microstructure of fatigue tested specimens thin foils of fatigue tested specimens were examined in the transmission electron microscope.;During fatigue deformation the average peak stress increased with increasing strain rate and grain size. It increased with decreasing temperature. It was almost independent of the plastic strain amplitude.;Interfacial sliding, interphase boundary migration, and intergranular cracking were detected on the surfaces of fatigue tested specimens. Interfacial sliding, which was almost reversible, occurred on (Al)/(Al) and (Zn)/(Zn) grain boundaries and on (Al)/(Zn) interphase boundaries. It did not occur at every grain boundary and interphase boundary, which suggested that grains slid in groups. Interfacial migration was detected at a few interphase boundaries that intersected the surface. Interphase boundaries usually migrated in the direction of the zinc-rich phase. Cracks followed grain boundaries and interphase boundaries. Along an intergranular crack most interfaces were (Zn)/(Zn) grain boundaries and (Al)/(Zn) interphase boundaries.;Grains deformed to accommodate interfacial sliding. Diffusional creep made a significant contribution to the deformation of grains of the zinc-rich phase. Deformation of the aluminum-rich phase involved the glide and climb of dislocations.;Such processes as Ostwald-ripening, interfacial migration, and precipitation of zinc in the aluminum-rich phase, which involve diffusion, occurred during fatigue deformation. They proceeded more rapidly during fatigue deformation than during annealing.